1. Field of the Invention
This invention relates to new and improved epoxide insulating resins, which utilize a combination of selected phenol accelerators and selected organotin latent catalysts, and which are non volatile, solventless and cold-blendable and also have low viscosity and long storage life.
2. Background Information
Organotin catalysts are well known in the insulating resin art as latent catalysts for epoxy resins, for example, U.S. Pat. Nos. 4,020,017 and 4,112,183 (Smith et al. and Smith), taught epoxy compositions containing organotin compounds with chlorine, hydroxide, acetate, butyrate, propionate or dimethylphosphate, as well as phenyl, naphthyl, Br or NO2 substituted aryl, and benzyl groups, among others, as components, and listed twenty nine preferred compounds. Smith et al., ""017, specifically excluded phenolic; anhydride or amine compounds from the epoxy, and utilized reactive diluents containing 1, 2 epoxy groups. Smith, ""183, required use of a solvent such as a ketone or aromatic hydrocarbon, preferably a dual solvent system, which had to be removed by heating at over 65xc2x0 C. (149xc2x0 F.), and lists about twenty six preferred organotin catalysts.
In U.S. Pat. Nos. 4,296,018 and 4,356,417 (both Smith et al.) the phenols catechol, C6H4(OH)2, and pyrogallol, C6H3(OH)3 were used with epoxy resins and organotin compounds, but both teachings required use of a solvent such as a ketone or aromatic hydrocarbon, preferably a dual solvent system, which had to be removed by heating at over 85xc2x0 C. (185xc2x0 F.). Both of these patents list seventeen preferred organotin compounds, and specifically exclude anhydride, amine, phenol or amide curing agents.
U.S. Pat. No. 3,716,598 (Markovitz) taught control of the cure rate of epoxy resins by use of specific bis(triorganotin) oxides, and from 0.1 to 15 wt. %, based on total epoxy resin system, of a phenolic accelerator, such as pyrogallol, hydroxy-benzaldehydes, catechol, resorcinol and hydroquinone, among others. The bis(triorganotin) oxide had the formula: (R1)3Snxe2x80x94Oxe2x80x94Sn(R2)3, where R was an alkyl, cycloalkyl, aryl, or alkaryl group. One preferred material was bis(tri-n-butyltin) oxide.
While all of these resinous epoxy insulating compositions each have their own advantages, what is still needed is a resinous system having a unique cure system that provides: (1) a solventless, cold-blendable resin admixture not requiring volatile and flammable monomers such as styrene or vinyl toluene (2) a low viscosity resin (below about 120 centipoise at 25xc2x0 C.) suitable for vacuum pressure impregnation (xe2x80x9cVPIxe2x80x9d in high voltage insulation for coils of motors and generators (3) a resin compatible with mica tape, and importantly, (4) a resin which has a long storage life and that does not require special equipment or pre-cooking, and which uses raw material components readily commercially available world-wide.
Therefore, it is one of the main objects of this invention to provide a high voltage capable insulating resin that can be manufactured with ease in almost any country without highly specially trained personnel or expensive oven equipment, and which, during manufacture, would have minimum emission health problems.
It is another main object of this invention to provide a solventless, cold-blendable, low viscosity insulating resin that can be used to impregnate mica tape in motor and generator coils.
These and other objects of the invention are accomplished by providing an insulating resin consisting essentially of: an epoxy system having an epoxy resin component and an epoxy reactive diluent having 1,2 epoxy groups in its chain structure; a phenolic accelerator selected from the group consisting of catechol, pyrogallol and mixtures thereof; and an organotin latent catalyst selected from the group consisting of triphenyltin chloride, tribenzyltin chloride, tribenzyltin hydroxide, triphenyltin acetate and mixtures thereof, where the insulating resin is solventless and has a viscosity of from 10 centipoise to 150 centipoise at 25xc2x0 C.
This means that the viscosity at 25xc2x0 C. will remain below 450 cps. for at least eight weeks. The insulating impregnating resin can be cold-blended at from 20xc2x0 C. to 35xc2x0 C. Preferably the epoxy resin component will be a cycloaliphatic epoxy resin or a blend of cycloaliphatic epoxy resin plus other type epoxy resins where the cycloaliphatic epoxy constitutes at least 50 wt. % of the blend. The preferred reactive diluent is the diglycidyl ether of neopentyl glycol. In all cases both cycloaliphatic epoxy and epoxy reactive diluent will be present in the epoxy system.
Preferably the reactive diluent will constitute from 30 wt. % to 70 wt. % of the epoxy system, the phenolic accelerator component concentration will range from 0.001 wt. % to 0.4 wt. %, preferably from 0.01 wt. % to 0.4 wt. %, of the insulating resin, based on the total weight of the epoxy system (epoxy resin component and reactive diluent). The organotin component concentration will range from 0.01 wt. % to 0.1 wt. %, preferably from 0.05 wt. % to 0.1 wt. %, of the insulating resin, based on the total weight of the epoxy system. Both the selected phenolic accelerator and the organotin catalyst must be present in the insulating resin.
These insulating resins have a long storage stability at 25xc2x0 C. of over about 4 months, and can be used to pot or encapsulate electrical components or to impregnate mica or glass tape used on coils for electrical machines, such as motors or generators. Where a xe2x80x9cmedium viscosityxe2x80x9d resin ranges from about 16,000 cps. to 20,000 cps., these ultra low viscosity resins (up to 450 cps. for eight weeks at 25xc2x0 C.) have excellent penetration ability and are excellent impregnating resins even after substantial storage. These resins are extremely easy to manufacture, utilizing a cold blending admixture of ingredients and not requiring a hot flash step for solvent removal, with attendant venting problems.